Waveguide



W. KRANK ET AL Oct. 1, 1968 WAVEGUIDE 2 Sheets-Sheet 1 Original Filed April 30, 1965 INVENTORS olfgang I 0rd Sc Erich Sch ATTORNEYS Oct. 1, 1968 w, KRANK ET AL 3,404,357

WAVEGUIDE Original Filed April 30, 1965 2 Sheets-Sheet 2 Fig.3

Fig. 5

INVENTORS Wolfgang Kronk Gerhard Sch ickle 8 Erich Schiittliiffel ATTORNEYS United States Patent 3,404,357 WAVEGUIDE Wolfgang Krank, Gerhard Schickle, and Erich Schuttloffel, Backnang, Germany, assignors to Telefunken Patentverwertungsgesellschaft m.b.H., Ulm (Danube), Germany Continuation of application Ser. No. 452,277, Apr. 30, 1965. This application May 1, 1967, Ser. N 0. 635,265 Claims priority, application Germany, Apr. 30, 1964, T 26,117; Dec. 18, 1964, T 27,645 12 Claims. (Cl. 333-95) ABSTRACT OF THE DISCLOSURE A flexible waveguide whose cross section is in the form of a flattened circle, the degree of flattening being just sufficient to prevent interfering wave types from occurring in the range of the desired operating frequency, the ratio of the minor axis of the waveguide cross section to the major axis thereof being at least 0.5.

This application is a continuation of parent case, No. 452,277, filed on Apr. 30, 1965, which application is now abandoned.

The present invention relates generally to the microwave art, and, more particularly, to a flexible waveguide for correctly transmitting an electromagnetic wave.

Waveguides having rectangular or circular cross sections have been used for a long time for transmitting electromagnetic waves. The waveguide with a circular cross section is not suitable for correctly transmitting an electromagnetic wave and therefore rectangular waveguides are generally used for this purpose. However, when a rectangular cross section is used it is very difficult to construct the waveguide to be flexible, while the round waveguide has the best flexibility because of its cross-sectional form.

Recently, a waveguide has been developed which is elliptical in cross section and can be wound on a drum. In this waveguide, there is a compromise between the mechanical stability or flexibility and the desired electrical characteristics.

It has been found that when using flexible waveguides having cross sections other than circular, more than just the flexibility of the waveguide itself is of decisive importance in most practical cases.

With this in mind, it is an object of the present invention to provide a flexible waveguide having suflicient flexibility and mechanical stability and which is dimensioned for optimum conditions regarding the relative bandwidth to be transmitted.

Another object of the invention is to provide a flexible waveguide of the character described which is so shaped as to prevent interfering wave types from occurring in the desired frequency range.

These objects and others ancillary thereto are accomplished in accordance with preferred embodiments of the invention wherein a waveguide is provided having a cross section which is noncircular and having cross section edges which are free of abrupt changes of direction. These edges are symmetrical to at least one of the two axes at right angles to each other and which axes have different lengths. Portions of the waveguide cross section are flattened and in some cases may be planar. This construction provides the waveguide with optimum dimensions regarding relative frequency bandwidth. In accordance with the invention the cross section is only flattened to a sufiicient degree to prevent interfering Wave types from occurring in the desired frequency range of operation.

3,404,357 Patented Oct. 1, 1968 Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a schematic view of the cross section of a waveguide indicating certain important dimensions thereof.

FIGURE 2 is a schematic cross section of an arrangement for transmitting two waves independently of each other.

FIGURE 3 is a schematic view of a waveguide which is loaded by a rectangular dielectric material.

FIGURE 4 is a schematic cross section of the wave guide of the present invention having a different shaped dielectric loading material.

FIGURE 5 is a schematic view illustrating the present invention having dielectric loading materials against both flattened surfaces thereof.

With more particular reference to the drawings, FIG- URE 1 shows the general shape of a waveguide constructed in accordance with the present invention and wherein the edges are flattened so as to be approximately planar. The major axis is indicated as D and the minor axis, which is perpendicular to this, is indicated as d. The length of the flattened portion is indicated as e. In the embodiment shown in FIGURE 1, the flattened portion is symmetrical to the major axis D.

As one feature of the invention, the waveguide is so dimensioned and based on relative frequency bandwidth which is to be transmitted that the following relationships are provided:

for d/D 0.5

where AF is the relative frequency bandwidth which is to be transmitted;

d is the small axis of the cross section;

D is the major axis of the cross section; and

e is the length of the flattened portion which is symmetrical to the major axis D, and the unit of length is millimeters.

If the waveguide is only flattened to such an extent as is permitted by the bandwidth, then, according to the above equation an optimum regarding attenuation is obtained when the value d/D 0.5 is 0.6 which is the peak of optimum conditions. This ratio d/D is always less than 1.0 because when attaining this value, the waveguide would no longer be flattened and therefore would not be suitable for correct transmission.

Regarding the embodiment shown in FIGURE 1, the bent portion of the cross section edges can generally have any shape. However, for simplifying production, the cross section should be as close to the circular form as possible. The flattened portions of the edges do not have to be planar; they can also be bent or slightly arcuate.

The flexibility of the Waveguide is obtained in the easiest manner by making it of a corrugated tube. The corrugations of the waveguide are preferably spiral-like and the waveguide is constructed with a longitudinal welding seam.

Radio installations frequently must send two waves simultaneously but independently from each other, to an antenna arrangement. In accordance with a further feature of the invention, two flattened waveguides can be joined together and arranged so that their flattened wall surfaces face each other, and with their axes parallel. They then together provide a unit. Such a waveguide arrangement is schematically shown in FIGURE 2. The two flattened Waveguides 1 and 2 are provided with a coating formed of a dielectric material 3. This unit provide sa Waveguide which can be easily mounted and permits the simultaneous transmission of two waves independently from each other and at optimum bandwidth. The two waveguides 1 and 2 can also be dimensioned for different frequency ranges.

A waveguide designed in accordance with the present invention can be produced in an easy manner by using the round waveguide and continuously deforming it until the desired cross section is provided. The corrugation in this case is then applied on the smooth round cross section.

Providing the correct dimensions to a flexible wave guide in accordance with the present invention makes it possible to correctly transmit maximally wide frequency bands without influencing the flexibility which is in practice required. Since the waveguide can be made of a corrugated tube, it is possible to produce any desired length of such a waveguide continuously.

FIGURE 3 shows an embodiment of the present invention wherein dielectric loading is used. The waveguide 8 of FIGURE 3 is provided with a dielectric material 4 which is located on the inside surface of a flattened wall of the waveguide. It is rectangular in cross section and does not cover the entire width of the waveguide.

In the embodiment of FIGURE 4, a waveguide 9 is provided and has a dielectric material 5 for loading it. This dielectric material is disposed on the inside surface of a flattened wall and in this embodiment the dielectric covers the entire width of this wall. The inwardly facing surface of the dielectric material is circular so that a circular segment shape is provided for the cross section of the dielectric load 5.

In the embodiment of FIGURE 5, the waveguide is loaded by two dielectric strips 6 and 7 disposed one on each of the inside surfaces of the broad or flattened sides of the waveguide. This makes it possible to provide the flattened portion e of shorter width so that the waveguide will be more flexible. The shortening of the flattened portion e is proportional to Vs. In this formula 6' is the effective relative dielectric constant of the dielectric loaded waveguide. In these embodiments of FIGURES 3 through 5, the dielectric load is substantially at a right angle to the electric field vector of the waves which are to be transmitted.

By tapering the dielectric load at the ends of the waveguide in a suitable fashion, a simpler arrangement for connectors of the terminals of apparatus to be connected thereto is provided, for then it becomes possible to match waveguide and terminals in an easy manner.

Another advantage of the use of such a waveguide is that by providing the cross-sectional form closer to that of a circle, a less deformed profile of the corrugations of the waveguide is provided. The reason for this is that the flattening is provided by pinching or squeezing a round waveguide in a corresponding cable-making machine. The less the waveguide is pinched, the less is the deformation of the corrugation profile so that the profile of the corrugation can be designed in such a manner that minimum reflections are obtained.

Thus, these embodiments of the invention provide an arrangement where, if special requirements need be met concerning the flexibility of the waveguide, one of the flattened sides of the waveguide can be coated with a dielectric material on its inside surface. The mechanical flattening of the circular cross section which is required for proper transmission can then be reduced so that the waveguide is more flexible.

Another feature of the invention is that the dielectric material can be formed in at least one continuous strip which is arranged in the direction of wave propagation. It is also possible to arrange the dielectric material 'at periodic distances.

If the waveguide is formedas a corrugated waveguide, the dielectric material will be arranged in such manner that it extends at least partly into the grooves of the waveguide profile. Since the waveguide is to be flexible, the dielectric material should be of a type which will not adversely influence the flexibility of the waveguide. Such a dielectric covering can, for example, be glued or sprayed onto the inside wall. The dielectric load of the waveguide makes it possible to reduce the flattening of the waveguide without interfering wave types occurring, and this can be provided by choosing a corresponding shape and/ or dielectric constant.

Our copending application Ser. No. 445,506, filed Apr. 5, 1965, now Patent No. 3,299,374, issued on Jan. 17, 1967, relates to a somewhat similar construction and illustrates certain details which are not shown in this application.

For the dielectric loading of the waveguide the material should be flexible like a foil or foamed strip of polyethylene (PE), polyvinyl chloride (PVC), tetrafluoroethylene resin (Teflon TFE).

It will be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

We claim:

1. A flexible waveguide for the correct transmission of an electromagnetic wave, comprising a waveguide tube having a cross section other than a circular shape, the cross-sectional edges being free of abrupt changes of direction, said edges being symmetrical to at least one of two perpendicular cross-sectional axes which are of different lengths so that the waveguide is optimally dimensioned regarding relative frequency bandwidth to be transmitted, said cross section being basically circular but flattened to a sufiicient degree so as to prevent interfering wave types from occurring in the range of the desired operating frequency and wherein d/D is at least 0.5, where d is the length along the minor axis of the cross section and D is the length along the major axis of the cross section, the following relationships existing bewherein AF is the relative frequency bandwidth which is to be transmitted, and e is the length of the flattened portion which is symmetrical to the major axis of the cross section, and the unit of length is in millimeters.

2. A waveguide as defined in claim 1 wherein the edges are so flattened that they are substantially planar.

3. A waveguide as defined in claim 1 wherein the waveguide tube is corrugated.

4. A waveguide as defined in claim 3 wherein the corrugation is spiral-like and the waveguide tube is welded longitudinally.

5. A waveguide as defined in claim 1 wherein a dielectric material is provided on the inside surface of one of the flattened sides.

6. A waveguide as defined in claim 5 wherein the dielectric material is in the form of a continuous stripe arranged in the direction of wave propagation.

7. A Waveguide as defined in claim 5 wherein the dielectric material is disposed at periodic distances.

8. A waveguide as defined in claim 5 wherein the tube is corrugated and the dielectric material extends at least partially into the grooves of the corrugation.

9. An arrangement as defined in claim 1 wherein d/D is substantially equal to 0.6.

10. A waveguide arrangement including two waveguides each having a waveguide tube, having a cross section other than a circular shape, the cross-sectional edges being free of abrupt changes of direction, said edges being symmetrical to at least one of two perpendicular cross-sectional axes which are of different length so that the waveguide is optimally dimensioned regarding relative frequency bandwidth to be transmitted, said cross section being flattened to a sufiicient degree as to prevent interfering wave types from occurring in the range of the desired operating frequency having the following relationships:

wherein AF is the relative frequency bandwidth which is to be transmitted, d is the minor axis of the cross section, D is the major axis of the cross section, and e is the length of the flattened portion which is symmetrical to the major axis D, the unit of length is in millimeters, and d/D is at least 0.5, said waveguide tubes being arranged so that they have adjacent flattened walls in face to face contact with each other and their axes are parallel, said waveguides being joined together to form a unit.

11. An arrangement as defined in claim 10, wherein a dielectric layer covers said two waveguides.

12. An arrangement as defined in claim 10 wherein the two waveguides are dimensioned to have different frequency ranges of operation.

References Cited UNITED STATES PATENTS OTHER REFERENCES Southworth, G. C.: Principles and Applications of Waveguide Transmission, 1950, Van Nostrand Co., N.Y.

180 relied on).

Valenguela, G. R.: The Cutoff Wavelengths of Composite Waveguides, in IRE Transactions on Microwave Theory and Techniques, July 1961, pages 363-364.

HERMAN KARL SAALBACH, Primary Examiner.

ELI LIEBERMAN Examiner.

L. ALLAHUT, Assistant Examiner.

Disclaimer 3,404,357.W0Zfgang Kmnk, Gerhm-d Schz'clcle and Erich Schuttlofiel, Backnang, Germany. WAVEGUIDE. Patent dated Oct. 1, 1968. Disclaimer filed Jan. 14, 1972, by the assignee, Telefunken Patentverwertwmgs G.'m.b.H. Hereby enters this disclaimer to claims 5, 6, 7 and 8 of said patent.

[Ofim'al Gazette June 13, 1972.] 

